Device for reading from or writing to recording media in disc form exhibiting unbalance

ABSTRACT

The present invention relates to a device for reading from or writing to recording media in disc form which has an unbalance compensation means.  
     The object of the invention is to propose a device of this type which has the smallest possible unbalance even when exchangeable recording media are used.  
     This object is achieved according to the invention by virtue of the fact that the unbalance compensation means is a centrifugal force generation means which generates a centrifugal force which is variable during operation. According to another aspect of the present invention, provision is made for the unbalance compensation means to be a positioning means for positioning the recording medium.  
     The field of application of the invention includes, inter alia, devices for reading from and/or writing to optical recording media such as CD, CD-ROM, DVD, DVD-ROM, DVD-RAM and the like.

FIELD OF THE INVENTION

[0001] The present invention relates to a device for reading from and/orwriting to recording media in disc form which has an unbalancecompensation means.

BACKGROUND OF THE INVENTION

[0002] A device of this type is disclosed in WO 84/01863. This devicehas a brushless DC motor as drive motor which causes the recordingmedium in disc form to effect a rotary movement. The recording medium issecured to the drive motor by means of a securing means, in this casethe motor hub. In order to obtain a rotary movement of the recordingmedium which is as free as possible from unbalance, the DC motor, as theunbalance compensation means, is designed in such a way that milling hasto be effected only once at one location in order to obtain unbalancecompensation. The device is constructed in such a way that no unbalancecan arise in the course of assembly, repair or the like.

[0003] The known device may be regarded as having the disadvantage thatfreedom from unbalance exists only when the recording medium in discform also has no unbalance at all. Although this can be ensured in thecase of hard disc devices, this is not so in the case of devices havingexchangeable recording media.

SUMMARY OF THE INVENTION

[0004] The object of the invention is to propose a device of theabovementioned type which has the smallest possible even whenexchangeable recording media are used.

[0005] This object is achieved by means of the measures specified in theindependent claims.

[0006] The invention provides for the unbalance compensation means to bea centrifugal force generation means which generates a centrifugal forcewhich is variable during operation. The advantage of such a dynamicunbalance compensation means consists in the fact that tolerances of therecording medium, tolerances in the securing thereof and also tolerancesof the drive motor are permitted to be relatively high without theunbalance caused thereby having a disruptive influence on the operationof the device, since this unbalance is compensated for by the dynamicunbalance compensation means and is adapted to possibly changingconditions even during operation. Recording media afflicted byunbalance, such as so-called shape CDs, for example, which under certaincircumstances do not have uniform mass distribution, can be played backwithout difficulty in a device according to the invention.

[0007] Another aspect of the present invention provides for theunbalance compensation means to be a positioning means for positioningthe recording medium. This has the advantage that the unbalance iscompensated for directly at its source. That proportion of the unbalancewhich is caused by the recording medium or the positioning thereof inthe device and, by its nature, cannot be compensated for during theproduction or service of the device is thus compensated for. Thepositioning means serves to position the recording medium in such a waythat the centre of mass of the said recording medium is oriented suchthat it is centred with respect to the axis of the drive motor or theaxis of rotation of the recording medium.

[0008] According to the invention, the positioning means has springelements and damper elements, which are arranged such that they aredistributed uniformly over the circumference of the unbalancecompensation means. This has the advantage that automatic centring ofthe recording medium relative to its axis of rotation is enabled as aresult of this. Spring and damper forces cancel one another out byvirtue of the uniformly distributed arrangement, and forces occurring inthe event of an unbalance act on the spring and damper elements in sucha way that the centre of mass of the recording medium is displacedtowards the axis of rotation. This is carried out at a relatively lowspeed of rotation which is matched to the spring and damper forces orproperties. The self-centred position of the recording medium issubsequently fixed and maintained.

[0009] According to the invention, the centrifugal force generationmeans has a mass element, which can be moved during operation. This hasthe advantage that the centrifugal force can be altered in a simplemanner by alteration of the position of the mass element. In this case,the mass element is advantageously arranged on a rotating part and in amanner such that it can move with respect to this part, with the resultthat a displacement of the mass element is accompanied by an alterationof the unbalance. The invention provides for the use of one or more masselements of this type. A single mass element is advantageously designedsuch that it can be displaced both radially and in the angular directionwith respect to the rotation of the rotating part. The use of two masselements has the advantage that they need be arranged such that they canbe displaced in each case only in one dimension, that is to say radiallyor in the angular direction, in order to be able to compensate for theunbalance. The use of a larger number of mass elements, for examplethree, four or more, leads to more uniform mass distribution also in thedirection of the axis of rotation. The higher symmetry that is obtainedfor these and even higher numbers such as, for example, six, eight,etc., contributes to reducing the wear and to simplifying production ofthe device.

[0010] The invention provides for two mass elements to be arranged suchthat they can move about the axis of rotation of the recording medium.This has the advantage that a change in the angular position of the masselements is easily possible by virtue of the arrangement allowingmovement about the axis of rotation. Since two mass elements areinvolved, the radial component of the mass distribution can also be setin a simple manner by a symmetrical change in the angular position ofthese mass elements. The mass elements advantageously have essentiallythe shape of a segment of a circle or segment of an annulus, inparticular the shape of a semicircle or of half an annulus. If there aremore than two mass elements, provision is made for correspondinglysmaller segments of a circle which together produce a full circulardisc, the consequence of this being the most uniform mass distributionpossible. The movable securing of the mass elements should be designedto be as compact as possible in order to disrupt the mass distributionas little as possible. Segments of an annulus have the advantage that agreater mass accumulation is present radially on the outside, which,given an identical additional mass, enables greater effectiveness thanin the case of radially uniform mass distribution. The axis of rotationis generally identical to that of the drive motor. The mass elements areadvantageously arranged in proximity to the recording medium in order tocompensate for the unbalance as close as possible to its source, andconsequently to minimize mechanical stresses on the spindle and thebearings thereof, and also to prevent the propagation of vibration ondevice or drive motor to the greatest possible extent.

[0011] A further refinement of the invention provides for a plurality ofsmall mass elements to be used which can be placed along a circumferenceor a radius of the centrifugal force generation means. This has theadvantage that a larger number of mass elements can easily be meteredand a high outlay in terms of mechanical holding is unnecessary, as aresult of which the centrifugal force generation means can be designedin a space-saving manner. The mass elements can advantageously be placedon a circumference which, in the radial direction, is relatively farremoved from the centre, since, at that location, their influence isrelatively large even when the total mass is relatively small. In thiscase, the mass elements are advantageously held by the centripetalforce, which is not present without rotation of the recording medium, inwhich case, however, unbalance compensation is not necessary either.

[0012] Instead of a circumference or a radius of the centrifugal forcegeneration means, it is likewise possible to use the circumference orthe radius generally of a rotating part, without leaving the scope ofthe present invention. The mass elements are advantageously designed asfine- or coarse-grained powder arranged, for example, in a closedcontainer, in order to avoid any loss, in air, a specific other gas, atexcess pressure or negative pressure, in a liquid or the like. Theindividual particles are advantageously of essentially spherical designso that they can be packed as densely as possible. It is advantageous,however, for them to have a flattened or rough surface in order toincrease the reciprocal friction and, consequently, to hold a positionwhich, once assumed, is classified as optimal.

[0013] The invention furthermore provides an adhesion element or aholding element to be arranged on the circumference and/or on the radiusof the centrifugal force generation means. This has the advantage that,in addition to the centripetal force, a holding force or adhesion forceis exerted on the mass elements, as a result of which the latter areheld in their set position even with a reduced rotational speed. Thissolution is advantageous particularly when the rotary movement of therecording medium is stopped without the latter being removed from thedevice. In the event of subsequent, renewed operation, the unbalancecompensation is then still preserved and it is possible to go over tointerference-free playback operation more rapidly. The adhesion elementis, for example, an adhering surface coating, for example an adhesivelayer, a layer of electrostatic charge, a magnetized layer in the eventof using magnetizable particles as mass elements, or another suitableadhesion element. The holding element is designed for example as a roughsurface, as a surface like a bed of nails, or as a differentlyconfigured surface, in which the mass elements are fixedly suspended orare caught. Cavities with openings arranged in the direction of rotationare advantageously provided as the holding elements. This has theadvantage that the mass elements are received and held therein. In orderto neutralize the mass distribution that has been set, acceleration inthe opposite direction is provided for example, as a result of which themass elements are removed from the cavities.

[0014] According to the invention, the unbalance compensation means hasa control means, which essentially follows the rotary movement of theunbalance compensation means. This has the advantage that the unbalancecompensation means and the control means concomitantly rotating with thelatter are at rest relative to one another, thereby making itunnecessary to transmit for example control information, energy, forceor mutual influencing from stationary to rotating parts or elements. Themechanical and electrical outlay are thus reduced, as, too, is the powerloss.

[0015] According to the invention, the control means is a lever element.This has the advantage that the control means is of mechanical design,does not require the supply of electrical energy and is simple torealize. Preferably, a plurality of lever elements, in particular onesof identical design, are used, one or else a plurality of lever elementsbeing provided for each mass element.

[0016] According to the invention, the lever element has a point ofaction on a rotating part, a further point of action on a stationarypart and also a point of action on a mass element. This has theadvantage that point of action and lever element are arranged anddesigned in such a way that relative displacements, caused by theunbalance, of the points of action on the stationary part and on therotating part initiate leverage which effects a displacement of the masselement in the opposite displacement direction to that caused by theunbalance.

[0017] Another aspect of the invention provides for the unbalancecompensation means to have a control means which is arranged such thatit is essentially stationary with respect to the device. This has theadvantage that a control means arranged fixed with respect to thehousing reduces the number of parts arranged such that they rotate and,consequently, the space requirement thereof. A control means arrangedfixed with respect to the housing has the advantage, moreover, thatsupply lines e.g. for the purpose of control, power supply, etc., fromthe housing are possible without difficulty on account of thearrangement fixed with respect to the housing. Furthermore access to anactuating means which is arranged fixed with respect to the housing ispossible without difficulty.

[0018] According to the invention, the stationary control means is abraking means, which influences the angular position and/or the radialposition of the mass element. This has the advantage that the control iseffected by a stationary braking means, and information and energytransmission can be realized in a simple manner. The braking means isadvantageously an electromagnetic coil which moves a brake lever intoone or two braking positions in which the mass element is braked. Forexample, the angular position of second mass elements is influenced,thereby enabling good unbalance compensation by means of a small numberof components.

[0019] According to the invention, the braking means influences apositioning gear mechanism with rotating elements which is part of theunbalance compensation means. This has the advantage that the elementsof the positioning gear mechanism are braked by the braking means and agearing movement is thereby initiated. In this case, with a suitabledesign of the positioning gear mechanism, a single mass element ispositioned in the radial direction and in the direction of rotation.

[0020] The invention furthermore provides for the braking means to bepart of an engagement means for the recording medium in disc form. Thishas the advantage that a component which is present in any case is usedfor the purpose of unbalance compensation in a phase in which it isinactive in any case. The part of the engagement means is advantageouslya lever by which another element, the so-called puck, is moved towardsthe recording medium or away from the latter. In this case, theunbalance compensation means is advantageously integrated in theengagement means. This has the advantage that the unbalance compensationmeans engages from the other side of the recording medium compared withthe drive motor, and this means that on the drive motor side, it is notnecessary to make any modifications to a device whose construction mayhave already been completed, and, nevertheless, the unbalancecompensation means can be integrated since structural space forarranging the unbalance compensation means is more likely to beavailable on the side remote from the motor.

[0021] According to the invention, the control means has along-range-force-generating element. This has the advantage that directmechanical contact between control means and mass element or otherrotating parts of the unbalance compensation means is unnecessary,thereby obtaining a reduction in friction losses. The long-range forcethat is provided is, for example, a magnetic force, generated by anelectromagnetic, for example, an electrostatic force or another forcetransmitted without direct contact. According to the invention, the masselement is a magnetizable mass element and thelong-range-force-generating element is a magnet. This has the advantagethat magnetizable mass elements, for example iron particles, areinexpensive materials which are simple to manipulate. Magnets, inparticular electromagnets, are likewise inexpensive to produce and, asmass-produced articles, have well-known properties. The magnetizablemass elements are positionally displaced by means of the magnet; forexample, when iron particles are used, they are attracted by means ofthe electromagnet, gathered and, with the drive motor rotating, releasedat an angular position which has been determined as suitable. They arethen pressed by the centrifugal force against an outer wall to which,for their part, they pass on the centrifugal force. The magnetizablemass element that is provided may be either an individual mass elementor a small number of individual mass elements, or else a large number ofmass elements, for example pulverulent mass elements. A magnetic fluidcan likewise advantageously be used in this case.

[0022] The electromagnet is advantageously arranged in such a way thatthe force acts essentially in the radial direction, which enables a flatdesign of the centrifugal force generation means. A compact design inthe radial direction is obtained when the electromagnet is arrangedabove or below the plane of the centrifugal force generation means, thatis to say when the force acts essentially in the axial direction. Asingle electromagnet serves to release mass elements if appropriate in ametered manner or at various locations. Two electromagnets are providedin order to release mass elements at different locations so that optimummass compensation, for example in accordance with two emplaceable masselements, is consequently obtained. The arrangement of three or moremagnets which are advantageously of smaller design and are arranged withhigher symmetry also lies within the scope of the invention.

[0023] According to the invention, the unbalance compensation means isan additional force generation means, which is advantageously along-range force generation means. This has the advantage of a lowermechanical outlay and, consequently, a reduced susceptibility tointerference, since a movable mass element is not necessary and thecentrifugal force is generated in a different way.

[0024] According to the invention, the long-range force generation meansis a magnetic field generation means. This has the advantage that amagnetic force is relatively simple to generate, and that it has no, oronly slight, interfering influences on other parts of the device. It isadvantageous for a plurality of electromagnets to be arranged in astationary manner, the said electromagnets exerting a force ofattraction on a magnetizable, rotating element. In this case, at leastthree electromagnets, but advantageously a larger number thereof, arearranged such that they are distributed uniformly over thecircumference. They are driven in such a way that a circulating magneticfield is produced which circulates at the rotation frequency of therotating element and, consequently, exerts a force having a constantdirection with respect to this rotating element. The field is generatedin such a way that this force has a magnitude and direction suitable forcompensating for the unbalance. Another advantageous refinement consistsin equipping the rotating element with one or more electromagnets andarranging permanent magnets on the circumference in a stationary manner,all of which permanent magnets have their north poles directed radiallyinwards, for example. This has the advantage that the rotation frequencyof the magnetic field generated always correctly corresponds to that ofthe recording medium and, consequently, specific regulation is notnecessary for this. The electromagnets are advantageously supplied withenergy inductively.

[0025] According to the invention, the magnetic field generation meansis integrated in the drive motor. This has the advantage that noadditional structural space is necessary for the magnetic fieldgeneration means in the device, and that this function is in any caseobtained in the drive motor designed as an electric motor. Given anelectronically commutated motor, a centrifugal force control signal isaccordingly superposed on the normal signal of the solenoids, with theresult that the circulating force which compensates for the unbalance isadditionally superposed on the circulating travelling field. Instead ofthe magnetic field generation means, it likewise lies within the scopeof the invention to integrate a general long-range force generationmeans in the drive motor.

[0026] The invention provides for a sensor and an evaluation means to bepresent in the device. This has the advantage that the requisitecentrifugal force is optimally determined and set in terms of magnitudeand direction. A slow run-up to the optimum value or rapid overshootingbeyond this optimum value need not be feared, therefore. Consequently,the optimum operating state is reached rapidly and reliably. Theevaluation means evaluates the sensor signal and determines the tractiveforce suitable for unbalance compensation.

[0027] According to the invention, the sensor is a vibration sensor.This has the advantage that the undesirable property caused by theunbalance is measured directly. In this way, the unbalance iscompensated such that minimum vibration is achieved. This applies, whena vibration sensor is used, even when other influences are superposed onthe unbalance and, therefore, optimum unbalance compensation possiblydoes not correspond to optimum vibration damping.

[0028] According to the invention, the unbalance compensation means hasa sensor element, an evaluation means and a centrifugal force generationmeans and/or a positioning means, which are all arranged on a rotatingpart of the device. This has the advantage that the unbalancecompensation means is arranged in a particularly space-saving manner,since an information flow between a rotating part and a non-rotatingpart is not necessary.

[0029] The said elements are advantageously designed as micromechanicaland microelectronic elements, so-called mechatronic elements.Accordingly, sensor element, evaluation means, centrifugal forcegeneration means and/or positioning means are all arranged on a singlemechatronic support element. The sensor is advantageously designed as arotation sensor. The positioning means and/or the centrifugal forcegeneration means are/is designed for example as micropump andmicrovalves interacting therewith, which displaces hydraulic masselements and/or positions the recording medium. Since, in someinstances, only relatively small masses are required for thecompensation, micromechanical elements can be used practically in thiscase. Energy is advantageously supplied by way of the electrodynamiceffect or coupling-in of radiation.

[0030] An inventive method for setting a variable centrifugal force of acentrifugal force generation means has the steps specified in theindependent method claim.

[0031] These steps have the advantage that a simple yet reliable methodis realized in this way for the purpose of setting a centrifugal forceand hence compensating for the unbalance which is caused in a device forreading from and/or writing to recording media in disc form as a resultof non-uniform mass distribution of the recording medium or inaccuratepositioning thereof in the device. In this case, the comparison of thedifference between present value and stored value is preferably effectedin terms of magnitude or by way of defined upper and lower thresholdvalues. In general, the change in the moment of inertia is preferablyeffected by changing the radius, but may likewise advantageously beobtained by changing the mass of the mass element.

[0032] A step d), addition of a mass element, is advantageously carriedout between steps c) and e) of the method. The addition may consist inthe actual insertion of a mass element from the outside into thecentrifugal force generation means; however, addition may likewise beunderstood to mean that a mass element is moved from a starting positionto a different suitable position.

[0033] Further advantages and refinements of the invention may begathered from the following description of advantageous exemplaryembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 shows a device according to the invention with unbalancecompensation means designed as positioning means in a first operatingposition;

[0035]FIG. 2 shows a sectional illustration of the device according tothe invention from FIG. 1 along the line AA;

[0036]FIG. 3 shows the device according to the invention from FIG. 1 ina second operating position;

[0037]FIG. 4a shows a basic illustration of an unbalance compensationmeans of a device according to the invention, in plan view;

[0038]FIG. 4b shows a device according to the invention with unbalancecompensation means in accordance with FIG. 4a;

[0039]FIG. 5 shows a flow diagram of a method according to theinvention;

[0040]FIG. 5a-f show unbalance-angle diagrams for elucidating the methodrepresented in FIG. 5;

[0041]FIG. 6 shows a device according to the invention with positioningmeans;

[0042]FIG. 7 shows a device according to the invention with centrifugalforce generation means for a mass element in a first embodiment;

[0043]FIG. 8 shows a device according to the invention in accordancewith FIG. 7 with two mass elements;

[0044]FIG. 9a shows a device according to the invention in accordancewith FIG. 7 in a second embodiment, in a sectional illustration;

[0045]FIG. 9b shows a device according to the invention in accordancewith FIG. 9a, in plan view;

[0046]FIG. 10 shows unbalance compensation means of a device accordingto the invention with control means in neutral position, which controlmeans follow the rotary movement;

[0047]FIG. 11 shows unbalance compensation means in accordance with FIG.10 in a compensation position;

[0048]FIG. 12 shows centrifugal force compensation means with aplurality of small mass elements, in plan view;

[0049]FIG. 13 shows centrifugal force compensation means in accordancewith FIG. 12, in a perspective view;

[0050]FIG. 14 shows part of a centrifugal force compensation means inaccordance with FIG. 12 with a long-range-force-generating element in afirst operating state;

[0051]FIG. 15 shows the said part in accordance with FIG. 14 in a secondoperating state;

[0052]FIG. 16 shows a device according to the invention with long-rangeforce generation means;

[0053]FIG. 17 shows centrifugal force generation means of the device inaccordance with FIG. 16; and

[0054]FIG. 18 shows an unbalance compensation means with elementsarranged according to the invention on a rotating part of the device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0055]FIG. 1 shows a basic illustration of a device according to theinvention. A recording medium 1 in disc form is secured on a discturntable 4 by means of a securing means formed from a centring pin 2and a holding element 3. The holding element 3 is, often referred to asa puck as well. The disc turntable 4 is made to effect rotary movementby a drive motor 5. The unbalance compensation means, which is apositioning means 6 in this exemplary embodiment, is integrated in thedisc turntable 4. A spring element 7 and a damper element 8 of thepositioning means 6 are evident, which engage on the drive shaft 9 ofthe drive motor 5, on the one hand, and on the disc turntable 4, on theother hand.

[0056] The drive motor 5 is arranged on a support element 10, on which ascanner 11 is likewise situated. Like all the other elements of FIG. 1,the scanner 11 is illustrated only diagrammatically. All that isillustrated diagrammatically of the components of the scanner 11 whichare known to a person skilled in the art is a lens 12 which is movableradially and vertically with respect to the plane of the recordingmedium 1. The support element 10 is connected to the housing (notillustrated) of the device via damper elements 13 in a manneressentially decoupled from vibration.

[0057] A lever 14 serves to lift off the holding element 3 and thusrelease the recording medium 1 for removal from the device. In itsposition illustrated in FIG. 1, in which it is in contact with therecording medium 1, the holding element 3 is pressed by magnetic forcesonto the recording medium 1. For this purpose, a magnet 15 is arrangedon the holding element 3 and a magnet 15′ is arranged on the centringpin 2. The lever 14 is moved in the direction of the arrow 16.

[0058] It may be assumed in the exemplary embodiment that the recordingmedium 1 in disc form is an optical recording medium, for example a CDor a DVD, which has circularly or spirally arranged data tracks whichare scanned by means of a light beam focused by the scanner 11 and thelens 12. In this case, the rotary movement of the recording medium 1 andthe mobility of the lens 12 and of the scanner 11 in the radialdirection make it possible for the light beam to follow the data track.The mobility in the radial direction is indicated by the arrow 17.

[0059] If the recording medium 1 has an unbalance, or if it is arrangedsuch that it is not exactly centred in the device, then an unbalance Uoccurs, for example in the direction of the arrow 18. The consequence ofthe unbalance U is that vibrations are transmitted to the scanner 11 viathe disc turntable 4, the drive motor 5 and the support element 10. Thelarger these vibrations are, the greater the radial movement of the lens12 is influenced. The vibration S is a function of the unbalance U; thefollowing holds true: S=f(U).

[0060] In order to compensate for an unbalance U caused by the recordingmedium 1 or its securing, the lever 14 is first of all held in theposition illustrated in FIG. 1, in which it is not yet completelylowered, and the drive motor 5 is caused to rotate. In this case, theforce engendered by the unbalance U acts on the disc turntable 4, whichtransmits this force to the drive shaft 9 via spring element 7 anddamper element 8. Since the disc turntable 4 and the drive shaft 9 areprovided with play relative to one another, the disc turntable 4 is inthis case displaced relative to the drive shaft 9.

[0061]FIG. 2 shows a section through FIG. 1 along the line AA. It isevident that a plurality of spring elements 7 are arranged such thatthey are distributed uniformly over the circumference, each springelement 7 being assigned a damper element 8 situated opposite on theother side of the drive shaft 9. The spring constants of the springelements 7 and the damping constants of the damper elements 8 arecoordinated with one another in such a way that they enable automaticdisplacement of the disc turntable 4 relative to the drive shaft 9 atleast at a specific rotation frequency which is set for the purpose ofunbalance compensation. As soon as the disc turntable 4 is in a centredposition with respect to the drive shaft 9, which is determined by meansof a sensor, for example, but may also be assumed to be reached after apredetermined period of time has elapsed, the lever 14 is lowered inaccordance with arrow 16′. It then assumes its lowered positionillustrated in FIG. 3. In doing so, a tip 19 of the lever 14 comes intocontact with the holding element 3 and, consequently, fixes the radialposition of the holding element 3 and of the disc turntable 4 connectedthereto via the centring pin 2 in the centred position, that is to saythe position in which the unbalance has been compensated. The rotationalspeed of the drive motor 5 can now be raised to the speeds which aresuitable for reading from or writing to the recording medium 1, withoutany fear that the disc turntable 4 will be displaced and, consequently,that there will be a renewed unbalance U≠0.

[0062] The remaining parts of FIG. 3, which are not specificallydescribed, correspond to those described with regard to FIG. 1. Therotation of the drive shaft 9 is transmitted via a drive pin 20, whichengages in a recess 21 in the disc turntable 4, to the latter and henceto the recording medium 1.

[0063]FIG. 4a shows a basic illustration of part of an unbalancecompensation means which can be arranged either in an unbalancecompensation means designed as positioning means or in an unbalancecompensation means designed as centrifugal force generation means. Inthis case, a section in accordance with, for example, FIG. 2 is onceagain illustrated diagrammatically, the disc turntable 4 beingsupported, on the one hand, on the drive shaft 9 by means of a springelement 7 and, on the other hand, by means of two adjustable positioningpins 23. The positioning pins 23 engage in holes 26 in the discturntable 4 and are provided with an external thread 24, which interactswith an internal thread 25 in the holes 26. In this way, by rotation ofthe positioning pins 23, it is possible to alter the distance betweenthe disc turntable 4 and the drive shaft 9, with lengthening of therespective hole. Consequently, suitable adjustment of the twopositioning pins 23 enables the disc turntable 4 to be centred withrespect to the drive shaft 9 in the sense of unbalance compensation.

[0064] Instead of the disc turntable 4, however, it is also possible, inaccordance with a further aspect of the invention, to arrange a masselement 27 such that it can be displaced with respect to the drive shaft9 by means of spring element 7 and positioning pins 23. In this case,the unbalance compensation means is not designed as positioning meansbut rather as centrifugal force generation means. In this case, namely,the positioning of the mass element 27 means that the position of therecording medium 1 is left unchanged, while the unbalance U caused bythe said recording medium is opposed by an opposite centrifugal force orunbalance U′ caused by corresponding displacement of the mass element27.

[0065]FIG. 4b illustrates this diagrammatically in a device according tothe invention, in a sectional illustration. The unbalance U, indicatedby the arrow 18, of the recording medium 1 is opposed by the unbalanceU′ or centrifugal force caused by the mass element 27 and indicated bythe arrow 18′. The remaining elements contained in FIG. 4b correspond tothose described with reference to FIG. 1 and FIG. 3 and, therefore, arenot specifically explained here.

[0066]FIG. 5 illustrates a flow diagram of a method according to theinvention. With regard to individual steps of the method illustrated inFIG. 5, diagrams are represented in FIGS. 5a to 5 f for the purpose ofclarification.

[0067] The method, illustrated in FIG. 5, for setting a variablecentrifugal force of a centrifugal force generation means begins in stepa) with the start of the setting procedure. In step b) a measured valueU_(n), which corresponds to an unbalance, is compared with apredetermined lower limit value U_(limit). If the measured value U_(n)is below the limit value U_(limit), the method branches to step o), theend of the setting procedure. Otherwise, in step c), the present valueU_(n) of the unbalance is stored as stored value U_(n-1).

[0068]FIG. 5a diagrammatically shows the disc turntable 4 which has anunbalance. The said unbalance is indicated in an exaggerated manner bythe mass point m_(u), which is situated at a distance r_(u) from thecentre of the disc turntable 4, axis of rotation. A force F_(u) isengendered by this unbalance. A mass element r₁ is situated at adistance r₁ from the axis of rotation. Its position is variable in thedirection of rotation, this being indicated by the arrow designated byφ. The arrow designated by n specifies the direction of rotation of thedisc turntable 4. In FIG. 5a, the moment of inertia m₁r₁ correspondingto the mass element m₁ is greater than the moment of inertia m_(u)r_(u)corresponding to the eccentric centre of mass m_(u), this beingindicated by the size of the points designated by m₁ and m_(u).

[0069]FIG. 5d corresponds to the illustration of FIG. 5a with thedifference that the relative sizes of m₁r₁ and m_(u)r_(u) are reversedin this case. The procedure for ascertaining a value corresponding tothe unbalance U_(n) corresponds to the method as far as step c).

[0070] In step e) the angular position of the mass element m₁ is changedby a first value. This is a predetermined positive value +Δφ in theexemplary embodiment. In step f) a present measured value U_(n) of theunbalance is compared with the stored value U_(n-1), and, if the presentvalue U_(n) is less than the stored value U_(n-1), the method branchesto step h). Otherwise, in step g), the angular position of the masselement m₁ is changed by a second value (which is negative in theexemplary embodiment) −2Δφ. In the exemplary embodiment, the magnitudeof this value is twice as large as that of the first, positive value. Ingeneral, however, it suffices if sign and magnitude do not correspond tothose of the first value +Δφ from step e).

[0071] In the subsequent step h), the difference ΔU between presentvalue U_(n) and stored value U_(n-1) is compared with a threshold valueΔU_(max). If the difference ΔU is greater than the threshold valueΔU_(max), the method branches to step c). Otherwise, in step j), thepresent value U_(n) is stored as stored value U_(n-1).

[0072] The angular position changes in accordance with the arrowdesignated by φ in FIG. 5a and FIG. 5d. FIGS. 5b and 5 e show a diagramin which unbalance is plotted against angular position. In this case,the two curves each correspond to a mass m₁ which is large and smallrespectively, with regard to m_(u). Each curve has a minimum, that is tosay an angular position at which the resultant unbalance is the least.This point is indicated in each case by an x, while the starting point,which, in general, does not coincide with the minimum of the curve, ismarked by an ★.

[0073] By optionally multiple iteration of steps c) to h), the angularposition of the mass point m₁ is changed in such a way that the minimumor a point near the minimum is reached. It has turned out to beparticularly advantageous to branch to step j) if the difference ΔU isbelow 5%.

[0074] In step k) the moment of inertia of the mass element m₁ ischanged by a first value +Δm₁r₁, which is chosen to be a positive valuein the exemplary embodiment. A comparison between the present measuredvalue U_(n) and the stored value U_(n-1) is then carried out in step 1).If the present value U_(n) is less than the stored value U_(n-1), themethod branches to step n). Otherwise, in step m), the moment of inertiaof the mass element m₁ is changed by a second value −2Δm₁r₁, whose signand magnitude do not correspond to those of the first value +Δm₁r₁ fromstep k). In step n) the difference ΔU between present value U_(n) andstored value U_(n-1) is compared with a lower limit value U_(limit). Ifthe limit value U_(limit) is exceeded, the method branches to step j),otherwise the end of the setting procedure is reached with step o).

[0075] These steps are illustrated in FIGS. 5c and 5 f by diagrams inwhich unbalance is plotted against moment of inertia. By changing themoment of inertia m₁r₁ from the starting point indicated by ★ to the endpoint indicated by x, complete or virtually complete compensation of theunbalance caused by the eccentrically arranged centre of mass m_(u) isobtained. In the simplest case, the distance between m₁ and the axis ofrotation is, for this purpose, reduced in accordance with FIG. 5c orincreased in accordance with FIG. 5f. However, a corresponding effectcan also be achieved by changing the mass m₁, for example by removing oradding mass elements. In general, any measure which correspondinglychanges m₁r₁ can expediently be used in this case.

[0076] It is advantageous to add a mass element m₁ in a step d) betweensteps c) and e), which mass element is then displaced, in the followingsteps, in the angular direction and radially in order to obtain thechange in the angular position and in the moment of inertia. Thiscorresponds to the introduction of the mass point m₁ at its startingposition in FIGS. 5a and 5 d.

[0077]FIG. 6 shows part of a device according to the invention withpositioning means for the recording medium 1. The drive motor 5 isillustrated, as is its drive shaft 9, which drives the disc turntable 4via a drive pin 20, which extends into a recess 21. In this case, theregion illustrated above the drive motor 5 is illustrated essentially asa section corresponding to the lines BB′B″ from FIG. 4a. The upper partof the drive shaft 9 has a radial distance from the disc turntable 4,and also from the drive pin 20 in the recess 21. This enables the discturntable 4 to be displaced radially with respect to the drive shaft 9.

[0078] The holes 26 with an internal thread 25 which are arranged in thedisc turntable 4 are evident. The external thread 24 of the positioningpins 23 engages in the internal thread 25. At their radially inner end,the positioning pins 23 have a head 29 provided with a toothed rim 28.The respective upper region of the head 29 in the figure engages in ahelical gearwheel 30, 30′, and the respective lower part engages in ahelical gearwheel 31, 31′. The helical gearwheels 30, 30′, 31, 31′ eachhave a toothed rim inclined downwards and upwards, respectively. Theyare connected to nested cylindrical elements whose respective other endshave radially outwardly protruding braking elements 32, 32′, 33, 33′. Attheir radially outer end, the braking elements 32, 32′, 33, 33′ eachhave an annular rim 34, which can be brought into contact with a brakelever 35, 35′ in order to brake the respective braking element 32, 32′,33, 33′ and hence the associated helical gearwheel. For this purpose,the brake lever 35, 35′ is actuated radially inwardly or radiallyoutwardly by a control element 36, 36′, for example an electromagneticactuator. The braking of the rotary movement of one of the brakingelements 32, 32′, 33, 33′ results in the braking of the respectivelyassociated helical gearwheel 30, 30′, 31, 31′, whereby the correspondingpositioning pin 23 is made to rotate and, consequently, shortens orincreases the distance between the disc turntable 4 and the drive shaft9.

[0079] By a suitable combination of the settings of the two positioningpins 23, it is thus possible, as described with regard to FIG. 4, to setany suitable position of the disc turntable 4. The recording medium 1,which is not illustrated in this case, is consequently displacedcorrespondingly via the centring pin 2.

[0080] In order to obtain enhanced vibration decoupling, both thecontrol elements 36, 36′ and the drive motor 5 are secured by damperelements 13′ to their respective holding elements, which are notillustrated here.

[0081]FIG. 7 shows a device according to the invention with centrifugalforce generation means, which has a mass element 27. Drive motor 5,drive shaft 9 as well as the helical gearwheels 30, 30′, 31, 31′arranged thereon, the associated braking elements 32, 32′, 33, 33′, theannular rims 34, the brake levers 35, 35′ and the control elements 36,36′, and also the positioning pins 23 correspond to those described withregard to FIG. 6 and are thus not specifically described here.

[0082] The drive shaft 9 is in this case connected directly to the discturntable 4 and the centring pin 2. The positioning pins 23 engage inholes 26 in a mass element 27, which essentially consists of a radiallyouter ring element 37 and a perforated disc 38 arranged thereon. In theexemplary embodiment, the radially inner region of the perforated disc38 bears in the axial direction on the helical gearwheel 30′ as well ason the centring pin 2, but is spaced apart in the radial direction fromthe drive shaft 9, thereby enabling mobility both in the radial and inthe angular direction. The mass element 27 has a recess 21′, in which adrive pin 20′ arranged on the disc turntable 4 engages. Drive pin 20′and recess 21′ are provided with play, with the result that mobility ofthe mass element 27 relative to the disc turntable 4 is ensured in thiscase, too. The play is essentially present in the radial direction.Drive pin 20′ and recess 21′ ensure that the mass element 27 is causedto rotate in a manner coupled to the disc turntable 4. Radialdisplacement and angular displacement of the mass element 27 ensue inthe manner described with regard to FIG. 6, in that case with regard tothe disc turntable 4. It goes without saying that the individualcomponents arranged on the drive shaft 9 are mounted as frictionlesslyas possible both with respect to the said drive shaft and with respectto one another and also with respect to the radially inner region of thedisc 38, in order to minimize friction losses.

[0083] Positioning pin 23, helical gearwheels 30, 30′, 31, 31′ and alsobraking elements 32, 32′, 33, 33′ together form a positioning gearmechanism 41 which serves for the positioning of the mass element 27and/or of the disc turntable 4 and, via the latter, of the recordingmedium 1.

[0084]FIG. 8 shows part of a device according to the invention withcentrifugal force generation means 42, which has two mass elements 27,27′. The main proportion of the mass of the mass element 27 or 27′ isarranged in a ring element 37 or 37′, respectively, which is adjoinedradially inwardly by a perforated disc 38, 38′, which, at its radiallyinner end, merges with a sleeve 39, 39′ mounted in a sliding manner onthe drive shaft 9 of the drive motor 5. The sleeves 39, 39′ are alsomounted such that they slide with respect to one another. Arranged onthe perforated discs 38, 38′ are drivers 40, 40′ which consist, forexample, of a rubber ring and normally ensure that the elements whichbear on them, namely disc 38 and disc turntable 4 and disc 38′ and disc38, respectively, do not move relative to one another. However, thedrivers 40, 40′ composed of elastic material do enable a relativemovement of the corresponding components when forces acting betweenthese components exceed a specific minimum value. Such forces areengendered by braking of one of the mass elements 27 or 27′ due todisplacement of a brake lever 35′ which comes into contact with anannular rim 34 of the corresponding mass element 27 or 27′. The brakelever 35 is activated by a control element 36′, as described with regardto the previous figures. Since two mass elements 27, 27′ which can beplaced independently of one another are involved in this exemplaryembodiment, only a single brake lever 35′ is necessary since the centreof mass formed by the two mass elements 27 and 27′ can be positionedfreely both in the angular position and in the radial direction byvirtue of the independent angular positioning of the individual masselements 27, 27′ themselves.

[0085]FIGS. 9a and 9 b show a device according to the invention withcentrifugal force generation means, which has a positionable masselement, in a further embodiment. FIG. 9a in this case shows a partiallysectional side view similar to FIG. 1, while FIG. 9b illustrates asection through FIG. 9a along the line CC.

[0086] In FIG. 9a, the parts corresponding to FIG. 1 are provided withthe same reference symbols and are not specifically described insofar asthere is no difference from FIG. 1. The disc turntable 4 is in this caseconnected directly to the drive shaft 9. The centring pin 2 is alsoconnected to the disc turntable 4 and has magnets 15′ at its upper end.The magnets 15′ interact with magnets 15 of the holding element 3, inorder to press the latter against the recording medium 1. The holdingelement 3 has a central stepped hole 43, through which a cylinder 44reaches whose lower end facing the centring pin 2 has a peripheralprojection whose external diameter is greater than the internal diameterof the step of the stepped hole 43. Movement of the cylinder 44 upwardsthus has the result that the peripheral projection comes into contactwith the step of the hole 43 and, as the cylinder 44 lifts further, theholding element 3 is driven and, consequently, the holding element islifted from the recording medium 1. In the position of the cylinder 44which is illustrated in FIG. 9a, the peripheral projection and the stepof the hole 43 are spaced apart from one another. The lower part of thecylinder 44 is in contact with a centring tip 45 of the centring pin 2,in order to ensure centring with respect to the drive shaft 9. The upperend of the cylinder 44 is likewise provided with a centring tip 46,which is centred in a centring recess 47 of the lever 14. The cylinder44 has a radial projection 48 below the centring tip 46. In the positionillustrated in FIG. 9a, the projection 48 is axially spaced apart from agripping element 49, which, during the lifting of the lever 14, comesinto contact with the projection 48 and, consequently, effects liftingof the cylinder 44. The cylinder 44 has a toothed rim 50 in its centralregion, which toothed rim is engaged with a toothed rack 51. The toothedrack 51 is part of a beam element 52, at whose ends a respective masselement 27, 27′ is arranged. The beam element 52 rests, on the one hand,on the holding element 3 and, on the other hand, is in contact with apressure plate 53. The pressure plate 53 is secured to the cylinder 44.

[0087] In the position of the lever 14 which is illustrated in FIG. 9a,the cylinder 44 and thus the pressure plate 53 are pressed downwards, asa result of which the beam element 52 is also pressed against theholding element 3. Relative movement of beam element 52 and holdingelement 3 is not possible in this position. If the lever 14 is raisedslightly, then although the beam element 52 and the pressure plate 53still rest on the holding element 53, relative movement is possible inthe event of the friction force being overcome. The effect of the lever14 being lifted further is that the gripping element 49 comes intocontact with the radial projection 48 of the cylinder 44, rotarymovement of the cylinder 44 thereby being braked. The result of this isthat the toothed rim 50 moves relative to the toothed rack 51 and,consequently, the beam element 52 is displaced in the radial direction.

[0088] This is indicated by the arrow 54 in FIG. 9b, which illustrates asection through FIG. 9a in accordance with the line CC. Arrow 55indicates a rotary movement of the beam element 52 which is obtained byheavy braking or heavy acceleration of the disc turntable 4 and hence ofthe holding element 3 and of the recording medium 1 in the slighlyraised position of the lever 14. In this case, a displacement in theradial direction in accordance with arrow 54 may also occur at the sametime, this being attributable to the interaction of toothed rim 50 andtoothed rack 51. By combining the two procedures described, it ispossible to displace the mass elements 27, 27′ both in their angularposition and in their radial position and, consequently, to compensatefor an unbalance U, see arrow 18, which is caused by the recordingmedium 1, for example.

[0089]FIG. 10 shows a diagrammatic illustration of an unbalancecompensation means 60 of a device according to the invention, which isarranged for example instead of the ring elements 37, 37′ and thecontrol element 36′ of FIG. 8 on a corresponding device. The unbalancecompensation means 60 is represented in a sectional plane arrangedperpendicular to the drive shaft 9 of the device. In the exemplaryembodiment, the unbalance compensation means 60 has four mass elements27, which are connected to a control means 61 composed of lever elements62, 62′ and 62″ and having points of action 63, 63′ on the unbalancecompensation means 60 and further points of action 64, 64′. The pointsof action 63, 63′ are arranged respectively in the outer and innerregion of a base plate 65 of the unbalance compensation means 60, whichbase plate is designed as an annular disc. The point of action 64 lieson a control casing 66, which is arranged such that it is fixed withrespect to the device and centred with respect to the drive shaft 9. Thefurther point of action 64′ is connected to the mass element 27. In theneutral position of the unbalance compensation means which isillustrated in FIG. 10, all the mass elements 27 have the same distancefrom the axis of rotation, that is to say from the drive shaft 9; anunbalance is not present. The base plate 65 has guide elements 67 bymeans of which the movably arranged mass elements 27 are guided in theradial direction. The base plate 65 rotates with the recording medium 1,that is to say with the same number of revolutions as the drive shaft 9,whereas the control casing 66 is stationary. The points of action 64 aremounted in sliding fashion, in rolling fashion or in another suitablemanner on the inner face of the control casing 66.

[0090] In FIG. 11, the base plate 65 is displaced eccentrically withrespect to the drive shaft 9 on account of an unbalance indicated by thearrow 18. Since the control casing 66 is undisplaced with respect to thedrive shaft 9, the points of action 63, 63′ located on the base plate 65have been displaced with regard to the point of action 64. The leverelements 62, 62′ and 62″, which are connected to one another in anarticulated manner, are tilted with respect to one another. Since thelever arm of the lever element 62″ is shorter than that of the leverelement 62, they are no longer parallel to one another in FIG. 11; theyare both tilted towards the centre point of the base plate 65.Consequently, the point of action 64′ on the mass element 27 is likewisedisplaced towards this centre point. This applies to the mass element 27illustrated in the upper part of FIG. 11. The guide elements 67 ensurethat the mass element 27 moves in the radial direction. The mass element27 represented in the lower part of FIG. 11 is displaced radiallyoutwards since in this case the corresponding lever elements arelikewise displaced away from the centre of the base plate 65. The masselements represented on the left and right in FIG. 11 are undisplaced inthe assumed direction of the unbalance. The lever arms of the leverelements 62, 62′,62″ and also the total length thereof and the mass ofthe mass elements 27 and also of the base plate 65 are designed in sucha way that the movement of the mass elements which is effected counterto the movement of the base plate 65 suffices to compensate for theunbalance. Instead of the four mass elements illustrated, it is alsopossible for three, five, six or a higher number of mass elements to bearranged correspondingly, without leaving the scope of the presentinvention.

[0091]FIG. 12 represents a centrifugal force compensation means 70 whichcan be arranged instead of the ring elements 37, 37′ of FIG. 8. It hasan annular cavity 71, which encloses a multiplicity of small masselements 27. The mass elements 27 are preferably iron particles or othersubstances having magnetic properties, for example a magnetic fluid. Inaddition to the mass elements, the cavity 71 contains a liquid or a gas,preferably of a defined composition. The cavity 71 is arranged such thatit is centred with respect to the drive shaft 9. In the right-hand partof FIG. 12, in a broken illustration, it is evident that anelectromagnet 72 is arranged as a long-range-force-generating elementunderneath the cavity 71. Arrow 73 indicates the direction of rotationof drive shaft 9 and centrifugal force compensation means 70.

[0092] As soon as the drive shaft 9 is made to move, the mass elements27 are accelerated towards the outer edge of the cavity 71 on account ofthe centrifugal force. At low speeds, the friction force may still begreater than the centrifugal force, with the result that the masselements 27 begin to move outwards only starting from a specific speedof rotation. The electromagnet 72 is activated in the accelerationphase, whereupon the mass elements, on account of the magnetic force ofattraction, accumulate on that wall of the annular cavity 71 which isadjacent to the electromagnet 72. In this case, the magnetic fieldgenerated by the electromagnet 72 is so strong that the mass elementsare all gathered on the electromagnet 72 despite the movement of thecavity 71. FIG. 12 accordingly shows a picture in which about half arevolution has already occurred since the electromagnet 12 was switchedon.

[0093] A centrifugal force compensation means 70 in accordance with FIG.12 is evident in FIG. 13, in a perspective illustration. In this case,two annular cavities 71, 71′ are arranged one above the other. Moreover,an electromagnet 72′ arranged radially on the inside is evident. Theelectromagnet 72′ serves to gather the mass elements 27 of the cavity71′, while a further electromagnet (not represented here) is arrangedeither likewise radially on the inside or underneath the cavity 71 inorder to gather the mass elements 27 located therein.

[0094] This is illustrated in FIG. 14. For the purpose of simplifcation,both alternatives, namely an electromagnet 72 arranged below or abovethe cavity 71 as well as a magnet 72′ arranged radially on the inside,are illustrated here. Both are in operation and have gathered the masselements 27. The inner wall of the cavity 71 is provided with astructured surface 75 on its outer circumference 74, which structuredsurface serves as adhesion element or holding element.

[0095] As soon as a recording medium has been inserted into the deviceaccording to the invention, the drive motor is switched on, as a resultof which the cavity 71 is made to effect the rotary movement. At thesame time, the electromagnet 72, 72′ is activated and the mass elements27 are consequently gathered. The unbalance of the rotating system,which is primarily caused by the unbalance of the recording medium, isdetermined by means of a sensor (not illustrated here) and acorresponding evaluation unit. In accordance with a suitable method, theposition at which the compensation mass ought to be arranged isthereupon determined. If the cavity 71 is in the corresponding angularposition, then the electromagnet 72, 72′ is switched off, whereupon themass elements 27 are accelerated and pressed against the outercircumference 74 on account of the centrifugal force. They remain thereon the structured surface 75. This is illustrated in FIG. 15. The masselements 27, preferably have a polyhedral or rough surface, with theresult that they adhere, on the one hand, to the structured surface 75of the cavity 71 and, on the other hand, reciprocally with respect toone another. More uniform distribution of the mass elements 27 over alarger region of the circumference 74 can be obtained by a definedreduction of the magnetic field strength generated by the electromagnet72, 72′.

[0096] The upper part of FIG. 15 illustrates the surface provided withcavities 76 having directed openings, with the result that in the eventof a direction of rotation corresponding to arrow 73, the mass elements27 are held in the cavities, even if the speed of rotation is reduced orbrought to zero. Accordingly, in the event of renewed acceleration,renewed positioning of the mass elements 27 is not necessary. For thepurpose of repositioning, rotation is momentarily effected counter tothe direction of the arrow 73, as a result of which the mass elements 27which were situated in the cavities 76 leave the latter and can begathered by the elecromagnet 72, 72′.

[0097] The second cavity 71′ shown in FIG. 13 serves for forming twoaccumulations of mass elements 27 in each of the two cavities 71, 71′.Something similar is likewise possible by arranging two electromagnets72 on a single cavity 71, but in this case it is more difficult toensure uniform distribution of the two mass elements on bothelectromagnets 72.

[0098] In FIG. 16, it is evident that the recording medium 1 rests onthe disc turntable 4 in a manner centred by the centring pin 2. Arrangedunderneath the disc turntable 4 is a rotor 81, which is part of theadditional force generation means 80 serving as unbalance compensationmeans. The rotor 81 is arranged on the drive shaft 9, which is driven bythe drive motor 5. The drive motor 5 is arranged on a support element 10which is arranged on a housing 82 via damper elements 13. A sensor 83and also the scanner 11 with lens 12 are furthermore arranged on thesupport element 10. Through an opening 84 in the housing 82, a scanningbeam (not illustrated here) passes from the scanner 11 through the lens12 onto the recording medium 1. The scanning of an optical recordingmedium of this type is generally known and, therefore, need not beexplained in any detail here. Furthermore, electromagnets 85 arearranged on the upper part of the housing 82, adjacent to the rotor 81,and are likewise part of the additional force generation means 80.

[0099] The sensor 83 serves to generate a signal which is related to theunbalance caused by the recording medium 1, for example. The sensor 83is a vibration sensor, for example. The output signal of the sensor 83is evaluated by a control unit 86, which determines from the said signalthe way in which the electromagnets 85 must be driven so as to generatea centrifugal force which counteracts the unbalance. For this purpose,the rotor 81 likewise has magnetic properties, for example permanentmagnets are arranged in it.

[0100]FIG. 17 shows a section in accordance with the line DD of FIG. 16.Part of the housing 82 is evident in which six electromagnets 85 arearranged. The rotor 81 is connected to the drive shaft 9 and arrangedsuch that it is centred with respect thereto. A narrow gap is presentbetween the rotor 81 and the electromagnets 85. In order to read from orwrite to the recording medium 1, the latter is made to rotate, driveshaft 9 and rotor 81 rotating in direction of the arrow 73. Any systemunbalance that may be present causes the rotor 81 to begin to vibrate.In order to compensate for this vibration, it is necessary to generate acentrifugal force which circulates at the frequency of the rotor 81 andacts in the opposite direction to the force engendered by the unbalance.The electromagnets 85 are provided for this purpose, the saidelectromagnets being driven by the control unit 86 in such a way that acirculating magnetic field is generated which generates thecorresponding compensation force.

[0101] In an alternative refinement, the lens 12 and the scanner 11 areused as vibration sensor instead of the sensor 83. The movement of thelens 12, which is also influenced, inter alia, by the vibrationgenerated by the unbalance, is determined by means of sensors present inthe scanner 11, for example photodetectors and a correspondingevaluation logic arrangement, and utilized for corresponding driving ofthe electromagnets 85. In a further alternative refinement of theinvention, a signal engendered by the circulating magnetic field whichcompensates for the unbalance is superposed on the electromagnets of thedrive motor 5, instead of the electromagnets 85. In a further refinementof the invention, the drivable electromagnets, indicated aselectromagnet 85′ in the lower region of FIG. 17, are arranged in therotor 81, which has the advantage that the frequency of the magneticfield generated by the electromagnets 85′ is always synchronous with thefrequency of the rotor 81.

[0102]FIG. 18 shows a diagrammatic illustration of an unbalancecompensation means 19 which, for example, is arranged at the position ofthe rotor 81 of FIG. 16 on the drive shaft 9. It has a sensor element93, which is designed as a vibration sensor and whose signal isevaluated by a control unit 96, which forwards an open-loop orclosed-loop control signal to centrifugal force generation means 91. Inthe exemplary embodiment, three such centrifugal force generation means91 are arranged such that they are distributed uniformly on theunbalance compensation means 90. In an alternative illustration, theupper right-hand part of FIG. 18 illustrates a positioning means 92,which is likewise arranged in an at least triple design distributeduniformly over the alternative configuration of the unbalancecompensation means 90.

[0103] The centrifugal force generation means 91 has a micropump 94,which is connected to a radially inner tank 95 and a radially outer tank95′. The micropump 94 is able to convey a fluid from the radially innertank 95 to the radially outer tank 95′, or vice versa. A displacement ofthe mass distribution of the unbalance compensation means can beobtained in this way. The mass distribution which is necessary forunbalance compensation can be obtained by joint interaction of aplurailty of centrifugal force generation means 91. The elementsillustrated in FIG. 18 are represented only diagrammatically; they arerealized for example as micromechanical components, so-calledmechatronic components, on a semiconductor support.

[0104] The alternative refinement with positioning means 92 also has amicropump 94′ which is connected to an outer tank 95″ and a pressurespace 97 of a pressure cylinder 98. The piston 99 of the pressurecylinder 98 is supported on the drive shaft 9, while the pressurecylinder 98 is secured to the unbalance compensation means 90. If fluidis conveyed from the tank 95″ into the pressure space 97 by themicropump 94′, then the distance between the unbalance compensationmeans 90 and the drive shaft 9 is increased at this point. The unbalancecompensation means 90 is consequently repositioned relative to the driveshaft 9, as a result of which an unbalance is likewise generated,artificially, which acts in the opposite direction to the unbalance ofthe system. The requisite force can be generated by a large number ofpositioning means 92, which are likewise designed as micromechanical ormechatronic components.

[0105] Although not all of the exemplary embodiments described haveevery expedient combination of features according to the invention, allthese combinations nevertheless lie within the scope of the invention,even if they are not expressly pointed out.

What is claimed is: 1) Device for reading from or writing to recordingmedia in disc form having a drive motor, a securing means and anunbalance compensation means, characterized in that the unbalancecompensation means is a centrifugal force generation means with acentrifugal force which is variable during operation. 2) Deviceaccording to claim 1, characterized in that the centrifugal forcegeneration means has a mass element, which can be moved duringoperation. 3) Device according to claim 2, characterized in that twomass elements are arranged such that they can move about the axis ofrotation of the recording medium. 4) Device according to claim 2,characterized in that a plurality of small mass elements are presentwhich can be placed along a circumference or a radius of the centrifugalforce generation means. 5) Device according to claim 4, characterized inthat an adhesion element or a holding element is arranged on thecircumference or on the radius of the centrifugal force generationmeans. 6) Device according to claim 1, characterized in that theunbalance compensation means has a control means, which essentiallyfollows the rotary movement of the unbalance compensation means. 7)Device according to claim 6, characterized in that the control means isa lever element. 8) Device according to claim 7, characterized in thatthe lever element has a point of action on a rotating part, a point ofaction on a stationary part and a point of action on a mass element. 9)Device according to claim 1, characterized in that the unbalancecompensation means has a control means which is arranged such that it isessentially stationary with respect to the device. 10) Device accordingto claim 9, characterized in that the stationary control means has abraking means, which influences the angular position or the radialposition of the mass element. 11) Device according to claim 10,characterized in that the unbalance compensation means has a positioninggear mechanism with rotating elements which can be influenced by thebraking means. 12) Device according to claim 10, characterized in thatthe braking means is part of an engagement means for the recordingmedium. 13) Device according to claim 9, characterized in that thecontrol means has a long-range-force-generating element. 14) Deviceaccording to claim 13, characterized in that the mass element is amagnetizable mass element and the long-range-force-generating element isa magnet. 15) Device according to claim 1, characterized in that asensor and an evaluation means are present. 16) Device according toclaim 15, characterized in that the sensor is a vibration sensor. 17)Device according to claim 1, characterized in that the unbalancecompensation means has a sensor element, an evaluation means and acentrifugal force generation means or a positioning means, which are allarranged on a rotating part of the device. 18) Device for reading fromor writing to recording media in disc form having a drive motor, asecuring means and an unbalance compensation means, characterized inthat the unbalance compensation means is a positioning means forpositioning the recording medium. 19) Device according to claim 18,characterized in that the positioning means has spring elements anddamper elements, which are arranged such that they are distributeduniformly over the circumference of the said positioning means. 20)Device according to claim 18, characterized in that a sensor and anevaluation means are present. 21) Device according to claim 20,characterized in that the sensor is a vibration sensor. 22) Deviceaccording to claim 18, characterized in that the unbalance compensationmeans has a sensor element, an evaluation means and a centrifugal forcegeneration means or a positioning means, which are all arranged on arotating part of the device. 23) Device for reading from or writing torecording media in disc form having a drive motor, a securing means andan unbalance compensation means, characterized in that the unbalancecompensation means is an additional force generation means, which has,in particular, a long-range force generation means. 24) Device accordingto claim 23, characterized in that the long-range force generation meanshas a magnetic field generation means. 25) Device according to claim 24,characterized in that the magnetic field generation means is integratedin the drive motor. 26) Device according to claim 23, characterized inthat a sensor and an evaluation means are present. 27) Device accordingto claim 26, characterized in that the sensor is a vibration sensor. 28)Method for setting a variable centrifugal force of a centrifugal forcegeneration means, having the following steps: a) start of the settingprocedure, b) comparison of a measured value, which corresponds to anunbalance, with a lower limit value and branching to step o) if themeasured value lies below the limit value, c) storage of the presentvalue as stored value, e) changing of the angular position of the masselement by a first value, f) comparison of a present measured value(U_(n)) with the stored value, and branching to step h) if the presentvalue is less than the stored value, g) changing of the angular positionof the mass element by a second value, whose sign and magnitude do notcorrespond to those of the first value from step e), h) comparison ofthe difference between present value and stored value with a thresholdvalue and branching to step c) if the threshold value is exceeded, j)storage of the present value as stored value, k) changing of the momentof inertia of the mass element by a first value, l) comparison of apresent measured value with the stored value and branching to step n) ifthe present value is less than the stored value, m) changing of themoment of inertia of the mass element by a second value, whose sign andmagnitude do not correspond to those of the first value from step k), n)comparison of the difference between present value and stored value witha lower limit value and branching to step j) if the limit value isexceeded, o) end of the setting procedure. 29) Method according to claim28, characterized in that the following step is carried out betweensteps c) and e): d) addition of a mass element.